1. Field of the Invention
This invention relates to sulfated fatty alkanolamide surfactants and more particularly to a process for producing fatty alkanolamides which are completely or almost completely sulfated.
2. Description of the Prior Art
Sulfated fatty alkanolamides were first synthesized some years ago and found to be effective detergents (U.S. Pat. Nos. 1,932,180 and 1,981,792). However, according to the prior art (Manufacturing Chemist 28, 124, 1957), it is extremely difficult to control sulfation to insure that the product is free of undesirable by-products which impair its efficiency as a detergent. It is well known that fatty alkanolamides are not usually sulfated maximally. Following are some of the difficulties that explain why they are so poorly sulfated: (1) the high viscosity of the molten alkanolamides prevents effective mixing with the sulfating agent; (2) the resulting unneutralized sulfated alkanolamides are even higher melting and much more viscous than the alkanolamides so that intimate contact with the sulfating agent is increasingly impeded; and (3) neutralization of such, hot viscous material is difficult and slow, and a substantial amount of hydrolysis may occur during this step. Although the viscosity problems can be partially alleviated by sulfation at high temperatures, this leads to charring and side reactions (U.S. Pat. No. 2,551,125). The viscosity problem can also be alleviated or even eliminated by the use of large amounts of inert solvents such as dichloroethane, methylene chloride, carbon tetrachloride or 1,1,1-trichloroethane. However, removal of solvents from such surfactant solutions is difficult and impractical on a commercial scale.
Consequently, even though the sulfated fatty alkanolamides are well known for their superior detergency and lime soap dispersing ability, they have not been produced in large volume because of the extreme difficulty in controlling the sulfation process to insure maximum sulfation and freedom of the sulfated product from undesirable by-products. With presently available processes, the maximum yield of sulfation is usually from 75-85% and the sulfated product contains large amounts of undesirable inorganic salts and organic by-products. As a result, these products exhibit inferior detergency and are not desirable for use in household detergents.